A fuel injector that includes a nozzle body which is tubular on its downstream side, and at whose downstream end a sealing seat and a spray discharge opening are positioned, is described in German Published Patent Application No. 198 49 210. The tubular portion of the nozzle body is insertable into a receiving bore of a cylinder head. The nozzle body is sealed with respect to the receiving bore of the cylinder head, which has a diameter corresponding to the radial extension of the nozzle body, with a seal that has approximately the geometry of a hollow cylinder.
For positional retention of the seal on the nozzle body, the nozzle body includes a circumferential groove which is made, for example, by turning down the nozzle body and into which the seal is inserted. Elastic materials that may be slid over the nozzle body for installation in the groove may be used as materials.
A further fuel injector, in which a sealing element is positioned on the nozzle body, is described in German Published Patent Application No. 198 08 068. The seal is made of a metallic material, and expands in the radial direction under the influence of the temperature created by the combustion process. This may be implemented either by manner of a shape-memory alloy or the use of a bimetallic seal. A groove in the nozzle body may be used for retention, as in the case of German Published Patent Application No. 198 49 210.
During operation of the internal combustion engine, the metal sealing ring heats up and expands. The sealing effect is thus enhanced during operation. For easier assembly, the metal seal has a slightly smaller diameter than the receiving bore that is introduced into the cylinder head for the fuel injector.
A disadvantage of the sealing approach described in German Published Patent Application No. 198 49 210 is the high temperature acting on the seal. With direct-injection internal combustion engines, full-throttle strength of nonmetallic seal materials may not be ensured.
The approach described in German Published Patent Application No. 198 08 068 has the disadvantage that the sealing effect of the metallic seal is temperature-dependent. After a cold start of the internal combustion engine, it takes some time for the materials in the vicinity of the combustion chamber to be heated by the combustion process sufficiently to reach, by thermal conduction, a temperature in the seal that results in the requisite geometrical change. In addition to the seal described, a further seal is used in order to seal the combustion chamber with respect to the exterior during initial operation of the internal combustion engine, so that compression pressure is not lost.
The complex materials that are used in the manufacture of metallic seals which deform in temperature-dependent fashion are also disadvantageous. A shape-memory alloy has a transition temperature matched to the application. Close tolerances in the manufacturing process are useful in guaranteeing this transition temperature. The result is to increase not only development costs for the alloy but also costs for utilization in series production.
The use of a bimetallic seal requires retention of the seal on a nozzle body, which serves as countermember upon deformation. Installation of the bimetallic element e.g. in a groove is difficult, however, since the properties of the metals change if one of the two metals experiences an inelastic deformation during installation